Semiconductor device testing method, using a spring-biased transformable conductive member electrode connection

ABSTRACT

An electrical connecting device and related method of testing a semiconductor device which provides testing of a semiconductor device under excellent and stable current transfer characteristics. Moreover, the electrical connecting device is easily produced under mass production conditions and can be made with a structure for testing of a semiconductor device where there are many pins arranged in a fine pitch on the semiconductor device. The electrical connector device includes a contactor which has a coil-shaped spring and a transformable conductive member extending in the compressing direction of the coil-shaped spring. When one end of the conductive member is in contact with a first electrode and the other end of the conductive members in contact with the second electrode, the contactor electrically connects between the first electrode and the second electrode via the conductive member and generates contact pressure against the electrodes when the coil-shaped spring is pressed. A guide plate is provided in the electrical connector device having a through hole for inserting and positioning the contactor therein. In a preferred embodiment, the semiconductor device to be tested has the first electrode for contact against one end of the conductive member of the contactor. The second electrode is a land pattern in a substrate of the electrical connecting device contacting the other end of the transformable conductive member, with the land pattern in turn being connected to testing equipment for testing of the semiconductor device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/104,332,filed Jun. 25, 1998, now U.S. Pat. No. 6,033,233.

This application is based upon and claims priority of Japanese PatentApplication No. 09-329106, filed Nov. 28, 1997, the contents beingincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to an electrical connectingmechanism for a semiconductor device and other electrical elements andmore particularly to a connecting device for electrical connection to anIC package in which many pins are arranged with a fine pitch, or a highspeed, high frequency IC, such as a bare chip, wafer or other electricalelement.

A contactor, such as a probe pin, has generally been used as a devicefor electrical connection to a semiconductor device and other electricalelements, particularly for testing purposes.

FIG. 1 is a diagram showing a structure of a probe pin in the relatedart. The probe pin shown in FIG. 1 includes a metal tube or pipe 200, acoil-shape spring 201, a metal end piece 202 and a terminal portion 203.The coil-shape spring 201 is provided within the metal pipe 200 and themetal end piece 202 is spring-biased in the upward direction of thedrawing by the spring force of the coil-shape spring 201. The metal endpiece 202 is provided to establish an electrical connection with anexternal electrode of a semiconductor device as the object of the testand the spring force produces a contact pressure between the metal endpiece 202 and the external electrode. The terminal portion 203 isconnected to testing equipment for testing the semiconductor device.

In the probe pin shown in FIG. 1, when the metal end piece 202 is incontact with an external electrode of the semiconductor device, acurrent flows to the terminal portion 203 via the metal tube or pipe 200from the metal end piece 202. Therefore, the probe pin itself must beformed in a fine structure in order to provide many of these pinsarranged to correspond with an IC package with many external electrodesarranged in a fine pitch. However, since the probe pin has acomparatively complicated structure, it is difficult to manufacture afine probe pin. Moreover, even if such a fine probe is formed, itbecomes very expensive.

Therefore, a probe pin as shown in FIG. 2 tends to be used recently. Theprobe pin of FIG. 2 includes a guide plate 210, a plurality of holes 211provided in the guide plate 210 and a plurality of coil-shape springs212 inserted into the holes 211. One end of the coil-shape spring 212 tobe used as a contactor is placed in contact with an external electrodeof a semiconductor device, while the other end of the spring 212 isconnected to a testing apparatus. This type of probe pin is formed in asimplified structure and therefore many coil-shape springs 212 can bearranged with a fine pitch.

In the probe pin having the structure shown in FIG. 2, a current istransferred via the coil-shape spring 212. If a certain turn of thecoil-shape spring 212 is not kept in contact with the next single turn,a current is transferred through a spiral path of metal wire of thecoil-shape spring. Therefore, a problem arises that resistance andinductance become large.

In the case of the structure of the probe pin shown in FIG. 2 where acertain turn of the coil-shape spring 212 is in contact with the nextsingle turn in many areas, resistance and inductance can be lowered.However, in this case, when the coil-shape spring 212 is compressed by acontact pressure from the external electrode, the contact condition of acertain turn and the next single turn changes, thereby resulting in adelicate change of a current transfer route. Therefore, a problem arisesthat fluctuation is generated in the current transfer characteristic inthe contact condition.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anelectrical connecting device having an excellent and stable currenttransfer characteristic.

It is a further object of the present invention to provide an electricalconnecting device that has a simplified structure, that can be readilymass-produced, and that can be arranged in a fine pitch.

It is a further object of the present invention to provide a method oftesting a semiconductor device under a condition of an excellent andstable current transfer characteristic.

Objects of the invention are achieved by an electrical connecting devicecomprising a contactor to electrically connect first and secondelectrodes and having a coil-shape spring, and a transformableconductive member extending in a compressing direction of the coil-shapespring, wherein one end of the conductive member is pressure contactablewith the first electrode and the other end of the conductive member ispressure contactable with the second electrode to electrically connectthe first and second electrodes when the coil-shape spring iscompressed; and a guide plate having a through hole in which thecontactor is positioned.

A current transfer path may be shortened and low resistance, lowinductance and stable electrical transfer characteristic may berealized, and a contact pressure may also be generated with a coil-shapespring by establishing the electrical connection between the firstelectrode and second electrode via the conductive member in place of thecoil-shape spring. Moreover, for electrical connection to asemiconductor device where many pins are arranged with a fine pitch, itcan be realized easily that the electrical connecting device can have aplurality of through holes in the guide plate provided with a fine pitchand a plurality of corresponding contactors can be inserted thereto andthereby a low price and high performance electrical connecting devicecan be provided.

Further objects of the invention are achieved by a method of testing asemiconductor device comprising: loading a semiconductor device having afirst electrode to an electrical connecting device, the electricalconnecting device having a contactor with a coil-shape spring, atransformable conductive member extending in a compressing direction ofthe coil-shape spring, wherein one end of the conductive member is incontact with the first electrode of the semiconductor device and theother end of the conductive member is in contact with a second electrodeto electrically connect the first electrode and the second electrodeswhen the coil-shape spring is compressed, and a guide plate having athrough hole in which the contactor is positioned; connecting testequipment to the second electrode of the electrical connecting device;executing a test to the semiconductor device through the secondelectrode; and removing the semiconductor device from the electricalconnecting device.

Since the stable and excellent electrical transfer characteristic can beprovided via the conductive member, high precision testing ofsemiconductor devices can be achieved and deterioration of an electricalsignal for testing can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe preferred embodiments, taken in conjunction with the accompanyingdrawings of which:

FIG. 1 is a diagram showing a structure of a probe pin in the relatedart.

FIG. 2 is a diagram showing another structure of a probe pin in therelated art.

FIGS. 3A and 3B are diagrams showing a contactor for an electricalconnecting device according to a preferred embodiment of the presentinvention.

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F, are diagrams showing further modifiedcontactors for an electrical connecting device according to preferredembodiments of the present invention.

FIGS. 5A and 5B are diagrams showing an electrical connecting deviceaccording to a preferred embodiment of the present invention.

FIG. 6 is a diagram showing an electrical connecting device according toanother preferred embodiment of the present invention.

FIG. 7 is a diagram showing an electrical connecting device according toanother preferred embodiment of the present invention.

FIG. 8 is a diagram showing an electrical connecting device according toanother preferred embodiment of the present invention.

FIGS. 9A and 9B are diagrams showing further modified contactors for anelectrical connecting device according to a preferred embodiment of thepresent invention.

FIG. 10 is a diagram showing a connection profile for an electricalconnecting device using the contactor of the type shown in FIG. 9A andFIG. 9B.

FIGS. 11A-11D are diagrams showing a method of manufacturing a contactorshown in FIG. 3A according to a preferred embodiment of the invention.

FIG. 12 is a diagram showing a structure for a semiconductor device testsystem using the electrical connecting device according to a preferredembodiment of the present invention.

FIGS. 13A-13C are diagrams showing a method for testing a semiconductordevice according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

In accordance with a preferred embodiment of the invention, and as shownin FIGS. 3A and 3B, there is provided an electrical connecting devicehaving a contactor 10. Contactor 10 of FIG. 3A includes an easilytransformable, elongated conductive member 11 and a coil-shape spring12. The conductive member 11 is provided within the coil-shape spring 12along the longitudinal direction thereof and, for example, is formed ofa metal wire to transfer current. At both ends of the conductive member11, metal balls 11 a or other similar disc-like contact elements areprovided. The coil-shape spring 12 is compressed, as shown in FIG. 3B,when the metal ball 11 a is in contact with an external electrode suchas that of a semiconductor to provide a contact pressure. In this casewhen the spring 12 is compressed, the conductive member 11 deforms asshown in FIG. 3B.

The metal ball 11 a has a diameter preferentially larger than theinternal diameter of the coil-shape spring 12. In this manner, theconductive member 11 is never or not allowed to be removed from thecoil-shape spring 12. Even when the coil-shape spring 12 is formed of aconductive material, current is transferred along the shortest routethrough the conductive member 11. Therefore, the coil-shape spring 12may be formed of either a conductive material or a non-conductivematerial.

As explained, in the contactor for the electrical connecting deviceaccording to the preferred embodiment of the present invention, thecoil-shape spring 12 provides elasticity to generate a contact pressure,while the transformable conductive member 11 provides a current transferroute. Since the route of the conductive member 11 is short, and inparticular shorter than through the coil-shape spring, an excellentcurrent transfer characteristic is realized resulting in smallinductance and resistance. Moreover, since the current transfer routedoes not change even during contact with the external electrode, astable current transfer characteristic also may be realized.

FIG. 4A to FIG. 4F show modifications to the contactor for theelectrical connecting device in accordance with preferred embodiments ofthe present invention. In the contactor 10A of FIG. 4A, both ends of theconductive member 11A are welded to the coil-shape spring 12. In thecontactor 10B of FIG. 12B, both ends of the conductive member 11B arefixedly hooked to the coil-shape spring 12. In the contactor 10C of FIG.4C, a plurality of conductive members 11C are provided and both endsthereof are welded to the coil-shape spring 12. In the contactor 10D ofFIG. 4D, the conductive member 11D is provided on the outside or at theexternal side of the coil-shape spring 12 and both ends thereof arewelded to the coil-shape spring 12. In the contactor 10E of FIG. 4E, theconductive member 11E is arranged on the outside of the coil-shapespring 12 and both ends thereof are fixedly hooked to the coil-shapespring 12. In the contactor 10F of FIG. 4F, a plurality of conductivemembers 11F are arranged on the outside of the coil-shape spring 12 andboth ends thereof are welded to the coil-shape spring 12.

The modified contactors of FIGS. 4A-4F operate and can achieve the sameor similar functions as the contactor shown in FIGS. 3A and 3B and asdescribed earlier. Particularly, for the contactors shown in FIG. 4C orFIG. 4F, when a plurality of conductive members are provided, resistanceand inductance of the current transfer route may further be reduced incomparison with the case where only one conductive member is provided.

An electrical connecting device is shown in FIGS. 5A and 5B and now willbe described hereafter in accordance with a preferred embodiment of theinvention.

As shown in FIG. 5A, electrical connecting device 18 includes contactors10, a guide plate 20, screws 22, screw stoppers 23 and a substrate 24.The guide plate 20 is provided with a plurality of holes 21corresponding to the positions of the external electrodes 31 of asemiconductor device 30 and contactors 10 are positioned in thecorresponding holes 21. Land patterns 25 are formed on one side of thesubstrate 24 to correspond with the holes 21 and contactors 10 locatedtherein as shown in FIG. 5B. The guide plate 20 is fixed to thesubstrate 24 with the screws 22 and screw stoppers 23. Where theelectrical connecting device 18 is applied to an IC package, the pitchof the electrical connecting device 18 can be 2.54 mm to as little as0.5 mm in a particularly fine pitch, and the quantity of contactorsaccordingly could be from 10 to as many as 1,000. Where the electricalconnecting device 18 is applied to a bare chip, the pitch of theelectrical connecting device 18 can be 0.3 mm to as little as 0.04 mm ina particularly fine pitch, and the quantity of contactors accordinglycould be a few to as many as a few thousands.

FIG. 5B is an enlarged view of portion “A” for the electrical connectingdevice shown in FIG. 5A. As shown in FIG. 5B, the contactors 10 arearranged within the holes 21 of the guide plate 20 so that thesecontactors 10 are in contact with corresponding land patterns 25. Asembodied herein, hole 21 has an inwardly tapered internal wall where theinternal diameter of the center area of the hole, for example, isnarrowed as shown in FIG. 5B. Accordingly, the contactor 10 is preventedto be removed from the hole 21. The land pattern 25 is provided with awiring 26 for connection with test equipment 49.

The electrical connecting device according to the preferred embodimentof the present invention can be electrically connected stably to theexternal electrode 31 of the semiconductor device 30 and thesemiconductor device 30 can be tested easily by the test equipment 49.Moreover, since the structure of the contactors 10 and guide plate 20 iscomparatively simple, it may be divided easily into small sections andit can be used with a semiconductor device 30 where a plurality ofexternal electrodes 31 are arranged in a fine pitch.

An electrical connecting device 18A according to another preferredembodiment of the present invention is shown in FIG. 6 and will now bedescribed. In FIG. 6, the elements like those elements for the device inFIGS. 5A and 5B are designated by like reference numerals and the sameexplanation is not repeated herein.

In the embodiment of the electrical connecting device 18A of FIG. 6, acontactor 10G is used in place of the contactor 10. In the embodiment ofthe device shown in FIG. 6, reliability of the electrical connection canbe improved by mechanical coupling between the contactor 10G and landpattern 25. The contactor 10G is coupled to the land pattern 25 at theend part of the contactor using a metal coupling means. Such a metalcoupling means, for example, could be a metal ball or disc-like element11 b fused using solder and fixedly coupled to the land pattern 25. Asanother example, a wire bonding technique can be applied. First, a ballat an end of a wire which is through a capillary is made using ahydrogen torch or electrical spark method. Next, the ball is secured atthe land pattern 25 by mechanical pressure from the capillary and afterthe securing step, the wire is cut with appropriate length. Next, acoil-shape spring is provided around the remaining wire on the landpattern 25. Finally, a metal ball 11 a is made using a hydrogen torch orelectrical spark method. However, the metal coupling means need not beso limited to these examples.

An electrical connecting device 18B according to another preferredembodiment of the present invention is shown in FIG. 7 and will no bedescribed. In FIG. 7, the elements like those elements for the device inFIGS. 5A and 5B are designated by like reference numerals and the sameexplanation is not repeated here.

In the embodiment of the electrical connecting device 18B in FIG. 7, twoguide plates 20A and 20B having a plurality of corresponding holes 27are stacked together. The corresponding holes 27 of the two guide plateshave stepped portions 27 a facing each other where the guide plates jointogether. Within the space formed by the stepped portion 27 a of theguide plate 20A and the respective stepped portion 27 a of the guideplate 20B, contactors 10H having connecting parts 11 c connected inseries are fitted therein. This arrangement prevents the contactor 10Hfrom being removed from its respective hole 27.

An electrical connecting device 18C according another embodiment of thepresent invention is shown in FIG. 8 and will now be described below. InFIG. 8, the elements like those elements for the device in FIG. 7 aredesignated by like reference numerals and the same explanation is notrepeated here.

In the embodiment of the electrical connecting device 18C of FIG. 8, twoguide plates 20A and 20B having a plurality of corresponding holes 27are again stacked together. The corresponding holes 27 of the two guideplates have stepped portions 27 a facing each other where the guideplates join together. Within the space formed by the stepped portion 27a of the guide plate 20A and the stepped portion 27 a of the guide plate20B, a relaying member 13 is fitted therein. Contactors 10I haveconnecting parts 11 c connected in series through the relaying member13. This structure prevents the contactors 10I from being removed fromthe holes. The method of securing between the metal ball of thecontactor 10I and land pattern 25 or relaying member 13 is the same asthe securing method for the embodiment of FIG. 6.

A contactor 10J and 10K having a modified structure for the electricalconnecting device is shown in FIG. 9A and FIG. 9B according to anotherpreferred embodiment of the present invention. In FIG. 9A and FIG. 9B,the elements of this contactor 10J and 10K that are like those elementsof the contactor 10 in FIG. 3A and FIG. 3B are designated by likereference numerals and the same explanation is not repeated herein.

Contactor 10J of FIG. 9A includes a conductive member 11, a coil-shapespring 12 and a metal end piece 14 connected to both ends of theconductive member 11 for contact. As shown in FIG. 9A, the metal endpiece 14 for contact has a recess 14 a and reliable electricalconnection can be established by fitting a ball type external electrodeof a Ball-Grid-Array (“BGA”) type semiconductor device into the recess14 a.

The further modified contactor 10K of FIG. 9B includes a conductivemember 11, a coil-shape spring 12 and a metal end piece 15 connected toboth ends of the conductive member 11 for contact. As shown in FIG. 9B,the metal end piece 15 for contact has a sharp end point 15 a andreliable electrical connection can be established by pushing the endpoint 15 a to a pin type external electrode of a Quadrille-Flat-Package(“QFP”) type semiconductor device and to the electrode like the landpattern 25 of the substrate 24 for the device of FIG. 5B.

In the contactors shown FIG. 9A and FIG. 9B, as explained above,reliable electrical connection can be established by providing the metalend piece for contact suitable for the shape of the electrode to beconnected. It is not required to provide a metal end piece for contacthaving the same shape at both ends of the contactor. For example, themetal end piece 14 for contact in the contactor of FIG. 9A can beprovided at one end and the metal end piece 15 for contact in thecontactor of FIG. 9B can be provided at the other end.

FIG. 10 is a schematic view showing a connection for an electricalconnecting device using a contactor having metal end pieces of the typesshown in FIG. 9A and FIG. 9B. In FIG. 10, the elements for the devicelike those in FIG. 5A and FIG. 5B, and FIG. 9A and FIG. 9B aredesignated by like reference numerals and the same explanation is notrepeated here.

In this electrical connecting device 18D of FIG. 10, contactors 10L havethe metal end piece 14 for contact provided at one end and the metal endpiece 15 for contact at the other end. Moreover, the recess 14 a of themetal end piece 14 for contact and the sharp end point or end part 15 aof the metal end piece 15 for contact are respectively provided with ametal plating 16 of Au to improve the electrical connection.

The ball-type external electrode 31 of the semiconductor device 30 ispositioned into the recess 14 a of the metal end piece 14 for contact,while the end part 15 a of the metal end piece 15 for contact is pushedinto contact with the land pattern 15 of the substrate 24. Thereby,reliable electrical connection can be established between the ball typeexternal electrode 31 of the semiconductor device 30 and the landpattern 25.

A method for manufacturing a contactor for an electrical connectingdevice in accordance with a preferred embodiment of the invention isshown in FIGS. 11A-11D and will now be described below.

As shown in FIG. 11A, in making the contactor 10 a wire 42 is fed from awire reel 40 and is then inserted into the inside portion of thecoil-shape spring 12 which is fixed to a clamping jig 41. FIG. 11B showsthe condition in the subsequent step where the wire 42 is inserted intothe coil-shape spring 12. In this condition and in the next step shownin FIG. 11C, the wire 42 is thermally cut at both ends of the coil-shapespring 12, for example, by a hydrogen torch method. The wire 42 also maybe thermally cut, for example, by an electrical discharging process.When the wire 42 is thermally cut, and as shown in the subsequent stepof FIG. 11D, the wire 42 is hardened in the form of a sphere at thecutting end, to provide the conductive member 11 inserted into thecoil-shape spring 12 and with metal balls or similar disc-like elements11 a at both ends of the conductive member 11.

As explained above, the contactor and the other components for theelectrical connecting device according to preferred embodiments of thepresent invention may be produced easily by simple processes which arequite suitable for mass-production.

As will now be described and as illustrated in FIG. 12, there isprovided an arrangement for semiconductor device test equipmentutilizing the electrical connecting device according to embodiments ofthe present invention.

The semiconductor device test equipment shown in FIG. 12 includes atester 50, a test head 51, a wiring 52 connecting the test head 51 andtester 50 and a contactor 53 using the electrical connecting deviceaccording to an embodiment of the present invention provided at the testhead 51. An LSI 60 is fitted to the contactor 53 to test the LSI 60, forexample a BGA type LSI, with the tester 50. The semiconductor devicetest equipment of FIG. 12 is available in the related art, except foruse of the electrical connecting device of the present invention, forexample, the embodiment of the device shown in FIG. 5A. Therefore, adetailed explanation thereof is omitted herein.

A method for testing a semiconductor device utilizing the semiconductordevice test equipment in FIG. 12 now be described in accordance with apreferred embodiment of the invention. The semiconductor testing methodis also illustrated in FIGS. 13A through 13C.

In FIG. 13A through FIG. 13C, the elements of the electrical connectingdevice used in this testing method that are like those elements of theelectrical connecting device in FIG. 5A and FIG. 5B are designated bylike reference numerals and the same explanation is not repeated here.

As shown in FIG. 13A, this testing method uses a contactor 53 whichincludes a guide plate 20 arranging contactors 10 corresponding to anarrangement of external electrodes 61 of LSI 60. The electricalconnection between the external electrode 61 and contactor 10 isestablished by inserting the LSI 60 into the contactor 53. FIG. 13Bshows the condition or subsequent step where the LSI 60 is inserted intothe contactor 53. Under this condition, various electrical tests areexecuted on LSI 60 using the appropriate test equipment. After the test,in the next step, the LSI 60 is removed from the contactor 43 as shownin FIG. 13C.

As explained above, this method of testing a semiconductor device can beexecuted under a stable and excellent electrical connecting condition,while the semiconductor device is loaded or unloaded easily. Theseadvantages of conducting the semiconductor device test according to theprocesses shown in FIG. 13A through FIG. 13C are achievable by using thesemiconductor test system shown in FIG. 12 provided with an electricalconnecting device according to the present invention.

Although a few preferred embodiments of the present invention have beenshown and described, it will be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A method of testing a semiconductor devicecomprising: loading a semiconductor device having a first electrode toan electrical connecting device, the electrical connecting device havinga contactor including a coil-shape spring and a transformable conductivemember extending in a compressing direction of the coil-shape spring,wherein one end of the transformable conductive member is in contactwith the first electrode of the semiconductor device and the other endof the transformable conductive member is in contact with a secondelectrode and the transformable conductive member is formed as a singlepiece structure from the one end to the other end thereof; using thetransformable conductive member to electrically connect the firstelectrode and the second electrode when the coil-shape spring iscompressed; positioning the contactor into a guide plate having athrough hole; connecting test equipment to the second electrode of theelectrical connecting device; executing a test of the semiconductordevice through the second electrode; and removing the semicondutordevice from the electrical connecting device.
 2. A method of testing asemiconductor device as set forth in claim 1, wherein metal members forcontact are provided at both ends of the conductive member in order torealize electrical connection between the first electrode and the secondelectrode.
 3. A method of semiconductor device as set forth in claim 2,wherein one of the metal members in contact with the first electrode tobe tested has a recess for fitting the first electrode projecting fromthe semiconductor device.
 4. A method of testing a semiconductor deviceas set forth in claim 3, wherein one of the metal members in contactwith the second electrode has a sharp end point pressing against thesecond electrode.
 5. A method of testing semiconductor device as setforth in claim 1, wherein the through hole has a tapered internal wallfor maintaining the position of the contactor therein.
 6. A method oftesting semiconductor device as set forth in claim 1, wherein aplurality of contactors are arranged in series within a plurality ofcorresponding through holes in contact with a plurality of firstelectrodes of the semiconductor device to be tested.
 7. A method oftesting semiconductor device as set forth in claim 6, comprising atleast two guide plates positioned together and having a plurality ofthrough holes with the stepped portions at sides of each of the twoguide plates positioned together, relaying members, and a least twocontactors arranged in the plurality of through holes of the at leasttwo guide plates and connected by the relaying portions in the steppedportions.
 8. A method of testing semiconductor device as set forth inclaim 1, comprising at least two guide plates positioned together andhaving a plurality of through holes with stepped portion at sides ofeach of the two guide plates positioned together and at least twocontactors arranged in the plurality of through holes of the at leasttwo guide plates and connected at corresponding ends in the steppedportions.